This invention relates to a clogged filter indicator of durable construction, low cost, and of simple installation which can serve as a visual or audible indication when an air filter is clogged. It is well known that a dirty air filter will reduce the efficiency of all air handling systems in which an air filter is employed to remove air borne contaminants. While the clogged filter indicator of this invention has general utility in most air handling systems employing a filter, it has particular utility in residential heating and air conditioning systems, and will be explained in that context.
In these times of concern over energy usage, much publicity has been directed at the public regarding the importance of keeping the air filter clean. A dirty air filter will greatly reduce the efficiency of operation of a heating and air conditioning system thereby increasing the cost of operation and wasting energy.
In the heating mode, a dirty air filter will reduce the air flow to the furnace heat exchanger causing it to operate at a temperature above its normal design range. This reduces the life expectancy of the furnace as well as wasting energy in the increased temperature of the flue gases leaving the furnace. Also, the system balance in the ductwork will be upset reducing the comfort level in the living space.
In the cooling mode, a dirty air filter will reduce the air flow to the evaporator coil thereby unbalancing the heat load between the evaporator and compressor. This can cause the evaporator to ice over further reducing air flow. Also, liquid refrigerant can flood back to the compressor causing damage to the compressor valves and bearings. Service records show that many expensive summertime service calls could have been avoided by the simple expedient of maintaining a clean air filter.
In spite of the wide publicity given to the need to maintain a clean air filter, field service experience indicates that in a majority of the cases, the public fails to properly maintain air filters. Consumer surveys also confirm this by noting that 80% of those surveyed do not periodically check the air filter. Remedial action is taken only after noting a secondary effect such as reduced air flow or high electric and gas bills.
It is clear from the above that a positive reminder in the form of a signaling device is needed to alert the consumer that the filter is dirty. In this manner, an important savings in energy and in reduced service costs can be effected.
A number of clogged filter sensing circuits have been invented as typified by U.S. Pat. No. 4,233,597, issued Nov. 11, 1980, to Gerhard Kurz, and U.S. Pat. No. 4,751,501, issued Jun. 14, 1988, to Edward B. Gut. The patent to Kurz shows a diaphragm responsive to the pressure differential across an air filter. Movement of the diaphragm beyond a predetermined pressure differential actuates a signal lamp. The patent to Gut shows a sensor to measure the pressure differential across a filter. The signal from the pressure differential sensor is combined with a rate of flow signal to actuate an alarm at a predetermined setting.
While the above-mentioned patents do teach dirty filter sensing circuits, the prior art does not teach a filter sensor having the simplicity of construction, the reliability, and the ease of installation found in the instant invention.